Virtualization of computing systems has become quite prevalent in recent times. It refers to a new layer that abstracts computer hardware from operating system (OS), and associated applications that run on it. Virtualization technique allows the computer hardware to support concurrent running of more than one operating system and applications associated with the operating systems held in containers called virtual machines, controlled and scheduled by a virtual machine monitor (VMM). This has offered a way for computer operators to consolidate, optimize and increase efficiencies of computing platforms while simplifying application deployment. To improve energy efficiency, virtual machines that are not currently operational are often powered off. Virtualization in general and powering off inactive VMs to save energy are in line with a green computing initiative that is becoming increasingly popular in various information technology domains. Such powered off virtual machines may need to be powered on upon a command from the system administrator for performing system maintenance. Using existing WOL technology to selectively power on computer systems is known. Providing WOL support in a virtualized environment, however, has its own challenges that will be described next. Before discussing WOL for virtualized environments a short introduction to the existing WOL technology is provided.
Wake-on-LAN technology is used by system administrators for doing maintenance on computer systems that are sleeping. Wake-on-LAN technology has been known since 1997, see, for example, “Wake-on-LAN” article from Wikipedia encyclopedia published on-line at http://en.wikipedia.org/wiki/Wake_on_lan, last modified Mar. 12, 2008, and White paper “White on LAN Technology” by Lieberman Software Corporation on published on-line on Jun. 1, 2006 at URL: http://www.liebsoft.com/whitepapers/pdf_files/Wake_On_LAN.pdf.
Many users turn off their computer systems (both desktop and server) at night to save energy. System administrators, however, need to do work at night, while users are away from their computer systems. Using the WOL technology, system administrators can wake up (power on) any number of sleeping (powered off) computer systems in minutes without making a physical visit to these computer systems. In this way they can make changes to multiple computers without impeding productivity of users who are not using their computers at that time.
Please note that although a computer system to be powered on is shutdown it has power to its network interface card (NIC) and some other parts of the computer system. Powering on the computer system in a Local Area Network (LAN) remotely, typically follows the following steps.                1. The NIC listens for a specific packet, called “Magic Packet” which is a broadcast frame represented in hexadecimal: FF FF FF FF FF FF followed by sixteen repetitions of a Media Access Control (MAC) address of the computer to be powered on. The Magic Packet is broadcast on a broadcast address for a particular subnet of LAN, or an entire LAN, in which case a special hardware and/or software/network configuration may be required.        2. The NIC receives this Magic Packet, checks it for correct information, and then turns on the main power of the computer system if the Magic Packet is valid and the MAC address of the NIC matches with the MAC address in the Magic Packet.        
FIG. 1 shows a block diagram 10, which illustrates the operation of the existing WOL technology. In FIG. 1 an Administrative System 12 is connected by a LAN 14 that includes a network switch 16 and computer systems 18, 20 and 22. Each computer system is running in V-Aux and is connected to a network switch 16 through a NIC. NICA 7, NICB 8 and NICC 9 respectively connect computer systems 18, 20 and 22 with the network switch 16. Each NIC has a MAC address abbreviated as MAC ADDR in FIG. 1. V-Aux refers to auxiliary power being sent to the NIC to keep it in a state in which it can receive the Magic Packet while rest of the computer is running on minimal power. First, the Magic Packet is broadcast from the Administrative System 12 on a LAN 14 (or a subnet of the LAN 14), the step of broadcasting being schematically shown as step {circle around (1)} in FIG. 1. The network switch 16 broadcasts the Magic Packet to all ports of computer systems connected to the LAN 14 (step {circle around (2)}). If a NIC on reserve power receives the Magic Packet containing its MAC address, it powers on the computer system (step {circle around (3)}). In this example, one or more of computer systems 18, 20, or 22 shown in FIG. 1 can be powered on in this way.
As discussed earlier, virtualization technology allows more than one VM comprising a Guest OS and applications to share a single computer system. Each virtual machine is provided with simulated computer hardware such that the Guest OS and application can run in isolation without making any modifications to them. Please note that VMs run on top of a virtualization platform which includes a hypervisor.
With all the advantages that have been offered by virtualization, it does not support the existing WOL technology as there is no NIC on reserve power for each VM listening for the Magic Packet.
Thus, there is an existing need in the industry for an improved and effective method for supporting Wake-on-LAN in a virtualized environment.